Apparatus and method for television reception



June 20, 1939. s. L. CLOTHIER ET AL 2,163,546

APPARATUS AND METHOD FOR TELEVISION RECEPTION Filed Oct. 8, 1937Patented June 20, 1939 UNITED STATES PATENT OFFICE APPARATUS METHOD FORTELEVISION RECEPTION Application October 8, 1937, Serial No. 167,912

7 Claims.

respective voltages for horizontal and vertical deflection of the ray berelatively high. In these tubes, the velocity of the electrons intravelling from the electron gun to the fluorescent screen is relativelyhigh in order to produceon the screen an image of sumcient brllliancyfor the projection and enlargement on the external screen. At therelatively high voltages it requires for this purpose, it becomesincreasingly difiicult to obtain a sharp electron focus at the screen.

With the foregoing in mind, it is one of the objects of our invention toprovide an improved apparatus and method for television receptionwhereby not only are the disadvantages of the prior constructions andmethods referred to avoided, but with our improved apparatus it ispossible to obtain much finer detail in the fluorescent image whilestill maintaining the necessary brilliance for optical projection onto alarge, external screen.

In accordance with our invention, we employ a cathode-ray receiving tubecomprising a. section in which the electrons travel ata relatively lowvelocity, and a section in which the electrons travel at a relativelyhigh velocity. First, in the low-velocity section of the tube a ray ofelectrons of comparatively low density and very small scanning-spot sizeis deflected to scan a given plane in this section and is simultaneouslymodulated in accordance with the incoming picture or video signals tocreate in said plane a. rela tively small but complete and true electronimage with relatively low velocity electrons and of fine texture ordefinition. The entire scanning operation and production of thiselectron image is accomplished at relatively low acceleratingpotentials. The true electron image so created is in effect a virtualcathode with respect to the highvelocity section of the tube and isemployed as such. Without further scanning deflection or modulation. butpurely by electron focusing and acceleration, a second electron image,which is a reproduction of the first, true electron image or virtualcathode, is produced at a fluorescent screen in the high-velocitysection of the tube, with the electrons traveling at relatively highvelocities to produce on the fluorescent screen a brilliant image forprojection by an optical lens system onto a large, external screen.

For the purpose of illustrating our invention,

an embodiment thereof is shown in the drawing,

in which:

Figure 1 is a simplified, diagrammatic view of television receivingapparatus constructed and operating in accordance with our invention;

Fig. 2 is an enlarged, fragmentary, sectional view showing amodification, the section being taken on the line 2--2 in Fig. 3;

Fig. 3 is an elevational view, looking toward 'the left in Fig. 2;

Fig. 4 is a view similar to Fig. 1, showing a modification; and

Fig. 5 is an enlarged, detail, sectional view,the section being taken onthe line 55 in Fig. 4.

With reference to Fig. 1, the reference numeral I designates atelevision receiving tube which is evacuated and comprises a section I Iand a section l2 of larger cross-sectional dimension than the sectionII. Mounted in the section II is means in the form of an electron gun I3 of a conventional construction for developing and modulating a ray I Iof electrons directed at a fluorescent screen 15 at the far end of thetube section l2. The ray I4 is focused on a plane l6 between thefluorescent screen 15 and the gun l3, at about the junction of theadjacent ends oi the tube sections H and I2.

The ray I l-of electrons is deflected simultaneously in horizontal andvertical directions by deflecting plates l1 and I8 in any suitable,conventional manner, whereby the ray I4 is caused to scan the plane IS.The ray is also modulated in accordance with the incoming video signalsby means of the conventional Wehnelt control electrode 25.

Disposed in the tube section I2 is an electronic lens system of anysuitable, conventional construction for the purpose hereinafterdescribed, and which in the presentinstance is shown as consisting ofmetal ring electrodes I9, 20 and II, and a metal disc electrode 22having a central opening 23, these electrodes being disposed as shownand in this particular case at substantially the potentials designatedin the drawing. The tube section I! may be provided on its innersurface, between the fluorescent screen l and the electrode 2 I, with acoating 24 of aquadag electrically connected to the electrode 2 l.

In the construction shown in Fig. 1, there is no material substance inthe plane I6 on which the ray I4 is focused and which is scanned by theray I4.

In the operation of our improved television receiving tube, aside fromthe facts that there is no fluorescent screen in the plane I6 to producethere a brilliant image forv projection and enlargement on a remote,external screen, and that the operating voltages are relatively low asdesignated in the drawing, the section II of our improved tube Illoperates in the same manner as a cathode-ray television receiving tubeof wellknown construction. That is, the picture signals are applied tothe control grid 25 to vary the ray intensity in accordance withoccurring variations in the incoming picture signals, and with the rayI4 focused on the plane I6 and deflected to scan this plane, a trueelectron image of the' view being televised is produced in the plane I6.In other words, if there were a fluorescent screen in the plane I6, avisible image of good definition would appear on such a screen.

The effect of the electronic lens system in the tube section I2 is tocause the electrons, from the elemental areas in the plane I6, to travelto the corresponding and respective elemental areas of the fluorescentscreen I5 and at a velocity substantially higher than the initialvelocity of the electrons at the plane I6. In other words, it might besaid that the electrons coming from the gun I3 are brought to a focus ata first focal plane such as the plane I6, to produce or develop in thisplane a true electron image of the view being televised, and that bymeans of the electronic lens system operating in accordance with thewell known principles of electron optics, the electrons passing on oremanating from the first focal plane I6 are greatly accelerated to avelocity substantially higher than the initial velocity of the electronsat the plane I6 and brought to a focus a second time at the fluorescentscreen I5.

Further in the above connection, it might be said that the electronimage in the first focal plane I6 is projected, by the electronic lenssystem, from the plane I 6 onto the fluorescent screen I5 remote fromthe plane I6. Also, in considering the principle, or manner of operationof our improved tube, it might be said that the electrons emanating fromthe plane I6 are refocused, but in an inverted relation as representedin Fig. 4, on a second remote plane, this in the'present instance beingthe plane in which the fluorescent surface of the screen I5 is disposed.In this manner the electron image developed in the plane I6 istransferred to the complementary surface of the remote fluorescentscreen I5, but with the electrons bombarding the screen I5 at a velocitysubstantially higher than the initial velocity of the electrons at theplane I 6, and with the brilliant image appearing on the fluorescentscreen I5 inverted with respect to the electron image developed in theplane I6. There is, therefore, produced on the screen I5 an invertedimage of good definition and which is of grea brilliancy. This image isprojected by a suitable lens system 26 onto a remote, external screen21.

It will be understood that the relative positions of the various partsand the repsective potentials onthe latter may be varied considerablyover the values designated.

In the modification shown in Figs. 2 and 3, a fine mesh, wire screen 28,which may be supported in a'mica frame 29, is mounted in the tube III,in the plane I6. It is proposed to first tre t the screen 28, such as byproviding it with a cesium silver oxide coating, to give it a relativelyhigh secondary-emissive characteristic. In the operation of thisconstruction, there is also developed a true electron image of the viewbeing televised at the plane of the screen 28. Some of the electrons ofthe ray I4 which pass through the screen 28, and electrons of secondaryemission from the screen 28, come to a focus at the corresponding andrespective elemental areas of the fluorescent screen I5 to produce onthe latter a brilliant, inverted image of good definition for opticalprojection onto the external screen 21'. The construction and operatingaction of the embodiment shown in Figs. 2 and 3 are otherwise the sameas in Fig. 1.

In lieu of using an electronic lens system con-' sisting of the ringsI9, 20 and 2|, and the disc 22, a single, elemental anode 30, as shownin Figs. 4 and 5, may be used for the same purpose, this being toproject or refocus the electron image in the plane IS on the fluorescentsurface of the screen I5, and to greatly accelerate the electrons axisof the tube section I2 and at the proper 1 point along this axis tofocus the electrons from the plane I6 on the fluorescent screen I5, inthe same general manner and according to the same principle disclosed inour pending application, Serial No. 161,730, filed August 31, 1937. Thatis, with elemental anode 30 at the high potential designated, theelectrons from any elemental area of the plane I6 are drawn to the anodeand are greatly accelerated during this travel so that they reach theanode at a relatively high velocity. While some of the electrons pass toground from the anode 30, many of them pass through the aperture 33 andpass on at the relatively high velocity and come to a focus on thecorresponding and respective elemental area of the fluorescent screenI5. In this manner, the electron image in the plane I6 is projected orrefocused, but'in an inverted relation as represented, on thefluorescent screen I5 to produce a brilliant, inverted image for opticalprojection and enlargement on the external screen 21.

Considering our invention from the broader aspect thereof, it will beseen that this resides in employment of a cathode-ray receiving tubecomprising a section I I in which the electrons travel at a relativelylow velocity and a section I2 in which the electrons travel at arelatively high velocity. Furthermore, the ray I4 in the low-velocitysection II and which is of comparatively low density and very smallscanning-spot size, is deflected and modulated to create in the plane I6a relatively small but complete and true electron image with relativelylow velocity electrons and of fine texture or definition. The entirescanning operation and production of this electron image is accomplishedat relatively low accelerating potentials. It will be seen that theelectron image so created is in effect a virtual cathode with respecttothe high-velocity section I! of the tube and is employed as such. Beyondthe plane [6, or in other words, in the high-velocity section l2 of thetube, there is no further scanning deflection or modulation, but purelyby electron focusing and acceleration, a second electron image, which isan inverted reproduction of for projection onto the large, externalscreen 21.

By means of our novel construction and method of operation, it ispossible to use very high accelerating potentials in the electron lens"section l2 of the tube, without the necessity for high deflectionpotentials and/ or high modulation potentials of the low-velocitysection I l. Further than this, instead of attempting, as heretofore, tosecure highest possible electron beam current and maximum electrondensity in a given size scanning spot at the fluorescent screen forsecuring the desired brightness, we employ electron beam current ofcomparatively low value and depend on the fact" that the effective massofthe electron increases tremendously at high velocities approaching thevelocity of light. As a direct result of this high velocity andincreased mass, the effect of theelectrons on the fluorescent screen istremendously increased. Even if a saturation condition exists such thatthe beam current is limited to only a few microamperes, regardless ofhow much the final anode potential is increased, it is still possible toproduce a greater surface brightness at the fluorescent screen, for a,given power expenditure, by employing extremely high velocities at thislow beam current than by employing high values of beam current, forexample, a few milli amperes, at correspondingly lower velocities.

It will be understood that various changesand modifications, within theconception of those skilled in the art, are possible without departingfrom the spirit of our invention or the scope of the claims.

We claim as our invention:

1. In a television receiving tube, 'a low voltage section and a highvoltage section. the latter including a viewing screen of fluorescentmaterialat the inside end wall of the tube and optically unobstructedfrom the tube exterior, means including an electron gun within the lowvoltag section developing from received electrical impulses representingpicture signals and at low velocity toward the low voltage section anelectron image ofthe viewabeing televised, said electron image being inadvance of the screen and apertured electrostatic electron lenselectrode means between said electron image and the fluorescent screenfor increasing the velocity of the electron beam and inverting andrefocusing the electron image at substantially the same size on thefluorescent screen said apertured means passing only an electron beam ofelemental size.

2. In a television receiving tube, a low voltage section and a highvoltage section, the latter including a viewing screen of fluorescentmaterial at the inside end wall of the tube and optically unobstructedfrom the tube exterior, means including an electron gun wthin the lowvoltage section developing from received electrical impulsesrepresenting picture signals and at low velocity toward the low voltagesection an electron image of the view being televised, said electronimage being in advance of the screen, and apertured electrostaticelectron lens electrode means between said electron image and thefluorescent screen constricting the electron beam to elemental size andinverting and refocusing the image at substantially the same size atincreased electron velocity on the fluorescent screen.

3. In a television receiving tube, a low voltage section and a highvoltage section, the latter including a viewing screen of fluorescentmaterial at the, inside'end wall of the tube and optically unobstructedfrom the tube exterior, means including an electron gun within the lowvoltage section developing from received electrical impulsesrepresenting picture signals and at low velocity toward the low voltage.section an electron image of the view being televised, said electronimage being in advance of the screen, and apertured electrostaticelectron lens electrode means between said' electron image and thefluorescent screen of minimum surface area and passing only an electronbeam of elemental size for inverting and refocusing the image atsubstantially the same size at increased electron velocity on thefluorescent screen.

4. In a television receiving tube, a low voltage section and a highvoltage section, the latter including a viewing screen of fluorescentmaterial at the inside end wall of the tube and optically unobstructedfrom the tube exterior, means including an electron gun within the lowvoltage section developing from received electrical impulsesrepresenting picture signals and at low velocity toward the low voltagesection an electron image of the view being televised, said electronimage being in advance of the screen, and including secondaryer'nissionmeans in the plane of said image, and apertured electrode meansbetween-said electron image and the fluorescent screen for increasingthe velocity of the electron beam and inverting and refocusing theelectron image on the fluorescent screen.

5. In a television receiving tube, a low voltage section and a highvoltage section, the latter including a viewing screen of fluorescentmaterial at the inside end wall of the tube and optically unobstructedfrom the tube exterior, means including an electron gun within the lowvoltage section developing from received electrical impulsesrepresenting picture signal and at low velocity toward the low voltagesection an electron image of the view being televised, said electronimage being in advance of the screen, and including secondary emissionmeans in the plane of said image, and apertured electrode means betweensaid electron image and the fluorescent screen for increasing thevelocity of the electron beam and inverting and refocusing the electronimage on the fluorescent screen, said apertured means passing only anelectron beam of elemental size.

6. In a television receiving tube, a low voltage section and a highvoltage section, the latter including a viewing screen of fluorescentmaterial at the inside end wall of the tube and optically unobstructedfrom the tube exterior, means including an electron gun within the lowvoltage section developing from received electrical impulsesrepresenting picture signals and at low velocity toward the low voltagesection an electron image of the view being televised, said electronimage being in advance of the screen, and including secondary emissionmeans in the plane of said image, and apertured electrode means betweensaid electron image and the fluorescent screen constricting the electronbeam to elemental size for inverting and refocusing the image atincreased electron velocity on the fluorescent screen.

7. In a television receiving tube, a low voltage section and ahigh-voltage section, the latter including a viewing screen offluorescent material at the inside end wall of the tube and opticallyunobstructed from the tube exterior, means including an electron gunwithin the low voltage section developing from received electricalimpulses representing picture signah and at low velocity toward the lowvoltage section an electron image of the view being televised, said,electron' image being in advance of the screen, and including secondaryemission means in the plane of said image, and apertured electrode meansbetween said electron image and the fluorescent screen of minimumsurface area and passing only an electron beam of elemental size forinverting and refocusing the image at increased electron velocity on thefluorescent screen.

STEWART L. CLOTHIER. HAROLD C. HOGENCAMP.

